Apr, * 5 » 1914 
37 
Coloration of Seed Coat of Cowpeas 
peroxid, or any of the alkaline carbonates demonstrate that one or more 
of the half-dozen tannins known to exist in plants are present in appre¬ 
ciable quantity in all the pigmented cells of the cowpea. But the optical 
color effect of this tannin is too small to need any attention here. What¬ 
ever r 61 e tannins may play in producing the pigments deposited in the 
cells, their chief service in the mature seed coat is undoubtedly protective. 
PIGMENTATION OF THE PALISADE LAYER 
The upper or palisade layer plays a most important part in the pig¬ 
mentation of the seed coat. As a rule, the cells are from 6 to 10 times 
as long as broad, with the cell cavity greatly enlarged at the lower or 
inner end, and gradually tapering upward to a mere thread at the upper or 
outer end of the cell (PI. VI, fig. 1, a , and text fig. 1, a ). From the central 
cavity, however, there radiate out into the gradually thickening walls 
from three to six vertical clefts, each reaching or nearly reaching the 
cell wall, thereby affording intercommunication between the cells. The 
result of this is that, looking on the cowpea seed coat from above, these 
cells appear to have at their outer end a stellate cavity (fig. 2). In 
focusing downward on the palisade cells these clefts gradually decrease 
by the widening of the central cell cavity until at or near the base the 
1 See an article on anthocyanin-forming bodies by Ioannes Politis, entitled <f Sopra speciali corpi cellular! 
che formano Antocianine,” published in Atti, R. Accad. Lincei, s. 5, Rend., Cl. Sci. Fis., Mat., e Nat., 
v, 20, sem. 1, p. 828 S34,1911. Politis here claims to have proved that anthocyanin is produced by certain 
special organs, cyanoplastids, in the composition of which tannin is a chief ingredient. 
